Abstract

Cortical dysplasia (CD) is considered to be a malformative lesion of the neocortex which exhibits a spectrum of pathologic changes reflecting a disturbance in the process of its development. CD is recently recognized as a major cause of intractable epilepsy with non-neoplastic lesions. Mischel et al. proposed that CD can be graded mild, moderate and severe with regard to nine specific microscopic abnormalities: mild CD consists of 1) cortical laminar disorganization, 2) single heterotopic white matter neurons, 3) neurons in the cortical molecular layer, 4) persistent remnants of the subpial granular cell layer, and 5) marginal glioneuronal heterotopia; moderate CD displays 6) polymicrogyria and 7) white matter neuronal heterotopia; severe CD phows 8) neuronal cytomegaly with associated cytoskeletal abnormalities and 9) balloon cell change. We reassessed 71 cases of cortical dysplasia to elucidate the proportion and histologic features of each group, using Mischel's grading system. CD was most frequently found in the temporal lobe with 50 cases (70%). Mild CD was predominently seen and was noted in 61 cases (86%) Cortical laminar disorganization and single heterotopic white matter neurons were identified in all mild CD cases. Neurons in the cortical molecular layer, persistent subpial granular cell layer, and marginal glioneuronal heterotopia were also noted in case numbers 40, 3, and 1 of mild CD, respectively. Moderate CD was composed of 2 cases with polymicrogyria, and the remaining 8 cases had severe CD. All moderate and severe CD were associated with the various histological features of mild CD. Thirty eight cases (51%) of CD showed dual pathology, composed of both CD and hippocampal sclerosis, and 5 cases of dysembryoplastic neuroepithelial tumor also had CD. Neurofilament immunostain revealed disarray of abnormally beaded axons in CD. We believe that the grading system of CD is very important to the evaluation and classification of CD.

• Keywords: Cortical dysplasia;Grading system;Pathology